Aromatic polyesters represented by polybutylene terephthalate and polyethylene terephthalate are excellent in mechanical property, electrical property and solvent resistance and are thus extensively used for applications to automobile parts, electrical and electronic parts and other mechanical parts. However, aromatic polyesters have problems in that they are low in heat deflection temperature under load and large in mold shrinkage and thermal expansion and so are not directly applicable to uses where they are subject to load under high temperature or required of strict dimensional stability. Therefore, the methods of incorporating glass fibers or any other reinforcements were proposed. But, such were shortcoming in that the molded products were inferior in surface appearance or had warpage and were not applicable to uses such as automobile exterior panel where the requirement for appearance or shape was strict.
On the other hand, polyphenylene ether is an excellent resin in heat resistance and dimensional stability. But, on account of its high softening point, it involved difficulties in melt processing, often decomposing during the melt processing. Therefore, it was usually used with styrenic resins blended. In these methods, however, there were some problems that the heat resistance was lowered and that the solvent resistance of polyphenylene ether, which was inherently not so good, would be further deteriorated.
Thus, various attempts were made to resolve the problems concerned with aromatic polyester and polyphenylene ether all at once by blending both polymers. As such method, there were proposed a method of adding a polyester to the polyphenylene ether (Japanese Laid-Open Patent Publication (Kokai) No. 49-50050), a method of blending a polyphenylene ether of a polymerization degree of 10 or higher to the polybutylene terephthalate (Japanese Laid-Open Patent Publication (Kokai) No. 49-75662) and a method of blending a polyphenylene ether to the polyethylene terephthalate (Japanese Laid-Open Patent Publication (Kokai) No. 59-159847). However, these methods merely of a simple blend of aromatic polyester and polyphenylene ether. Therefore, while the polyphenylene ether would have the moldability and solvent resistance improved and the aromatic polyester have the deflection temperature under load and dimensional stability improved, the adhesion between both polymers was not so good, and so there were provided only resins being inferior in surface appearance of molded article and mechanical properties including the impact resistance, and the methods were not practically applicable. Furthermore, for improvement of the adhesion between aromatic polyester and polyphenylene ether, there were proposed a method of concurrently using a styrenic resin containing the epoxy radical as a third component in Japanese Laid-Open Patent Publication (Kokai) No. 60-221459 and a method of further using a phenoxy resin and an unsaturated carboxylic acid in Japanese Laid-Open Patent Publication (Kokai) No. 60-258249. However, according to these methods, the adhesion between aromatic polyester and polyphenylene ether would be improved but slightly, while the composition had the heat resistance degraded and, according to the former method, had the melt viscosity increased. Thus, there has been provided no resin composition exhibiting the good properties of aromatic polyester and polyphenylene ether synergistically.